High-vacua pump



' May 4 1926.

R. BERRENBERG I HIGH VACUA PUMP Filed Dec. 26, 1924 TOR.

' fication.

Patented May 4, 1926.

UNITED STATES REINOLD BERRENBERG, OF BOSTON, MASSACHUSETTS.

HIGH-VACUA PUMP.

Application filed December 26, 1924. Serial No. 758,002.

To all whom it may concern:

Be it known that I, Ransom) BERRENBERG, a citizen of the United States, residing at Boston, in the county of Suffolk and State of Massachusetts, have invented certain new and useful Improvements in High-Vacua Pumps, of which the following is a speci- This invention relates to that class of rotary pump apparatus designed to produce an extremely high degree of rarefaction and more particularly to metallic pumps for producing high vacua.

High vacua are finding a rapidly extending application in numerous branches of industry and it is highly important that effective means be provided for securing vacua.

High vacua is required for exhausting nitrogen lamp bulbs, vapor lamps, mecury arc rectifiers, X-ray tubes, thermos bottles etc., and to be effective the pump must combine with a high capacity, a high limiting vacuum. A comparatively new field in which highvacua pumps are necessary is radio, in which field the present invention is particularly efiicient for evacuating the tubes used in that art for detecting and amplifying.

The object of the present invention is to provide a high-vacua. pump of extreme simplicity of construction which is relatively cheap to manufacture and yet will produce and maintain a practically perfect vacuum.

In carrying out-the object of the invention the type of pump selected is that embodying an eccentric rotor within the pump cylinder,

two such pumps being connected in series,

or tandem arrangement, so that what the first may lose the other takes up, and a single vane or abutment continuously engaging both rotors. By this means a final pressure of 0.0001 mm. of mercury, measured on a McLeod gauge, is readily obtained with a tandem pump the cylinders of which are only two inches in diameter.

To the accomplishment of this object and such others as may hereinafter appear as will readily be understood by those skilled in the art, the invention comprises the features and combinations of parts hereinafter described and then particularly pointed out in the appended claims.

The preferred form of the invention is illustrated in the accompanying drawings in which Figure 1 is a view, in side elevation, with the front cover of the tank removed; Fig. 2 is an enlarged view, in vertical longitudinal section, through the center of the pump cylinders; Fig. 3 is a diagrammatic view illustrating the manner in which the rotors are turned to final shape; and Fig. 4 is an end view of the sliding vane removed from the pump.

In the embodiment of the invention illustrated on the drawings an air tight tank 2 is provided, having a removable cover (not shown) and flanges 4 for lag screws or bolts. Within the tank on its bottom 6 are rectangular bosses 8 and 9 with finished upper surfaces to support the pump casing 10. The pump casing comprises two cylindrical rotor chambers 12 and 14 both in one casting Which forms a tangent, or Siamese, partition wall 15 between them. A boss is cast on the under surface of each rotor chamber and these are finished to engage the floor bosses, the casting being bolted in position as shown by Fig. 2.

Within the chambers 12 and 14 are the rotors 16 and 18 respectively.- Rotor 16 is mounted eccentrically on a shaft 20 which is ournaled in the front plate 22 and a rear plate (not shown). Rotor 18 preferably of the front plate 22, the teethof which meshwith the teeth of a central gear 30 which rotates idly on a stub shaft 32 carried by the front plate. The shaft 24 rotates in a manner to drive the rotor 18 in a clockwise direotion and the gearing causes the rotor 16 to be driven in the same direction.

The tangent partition wall is cut through from side to side forming a horizontal slot 33 adapted to receive asliding vane or rotor abutment having ends 34 and 36 engaging the circumferential surfaces of the rotors 16 and 18 respectively. The slot is deeperrthan required to'receive the vane which has a slide leg-37 (Fig. 4) at each end bearing on the lower wall of the slot and maintaining the I shafts 20 and 24 thus permitting the centralplane of the vane to he in the plane of said axes when constructed and mounted as described. The passage between the vane legs forms a horizontal port below the vane, that connects the rotor chambers 12 and 14. The pum casing has a central boss 40 at its top whic is cored during manufacture to produce inlet and outlet ports. The course of the air passing through the pump is indicated by arrows a, b and c. I

' A nipple 46 spans the space from boss 40 to the tank cover and, after passing themthrough, is joined to a tube 42 leading to the article to be evacuated, all as shown in Fig. 2. The tank is also provided with an opening 44, closed by a screw cap, through which the lubricant may be introduced and the air, discharged from the port 6, permitted to escape. The rotors 16 and 18 are of special form and effectually prevent leakage of air back.

to the article being evacuated. In order to prevent such leakage it is essential that communication between the ports a and c be absolutely prevented and likewise between the ports I) and 0. This function of perfect disconnection between any two adjacent air ports is attained by specially forming the circumferential surface of the rotor members 16 and 18.

Heretofore, the. rotors, in pumps of the tvpe described, have been true cylinders t ereby ofiering merely a line contact with the inner wall of the rotor chamber. With such a rotor contact in the pump of the present invention it is obvious that, at the time the sliding vane bears on the point of greatest rotor eccentricity (see position of rotor 18, Fig. 2), the inlet and outlet ports communicating with the rotor chamber will be connected through the air chamber at the other side of the eccentrically mounted rotor. This permits the previously evacuated air to leak back, at each revolution of the rotor, through the port a and passage 46 or from the'c amber of the second pump stage back into the chamber of the first P p ag I In accordance with the present invention the disadvantage of leakage is eliminated by providing a surface contact, instead of a line contact, between the rotor and its chamber wall. This surface is -of suificientangular length to extend across and seal both ports at each side of the sliding-vane when either rotor is in the angular position illustrated' by the rotor 18 in Fig. 2, and to keep one port sealed until the sliding vane becomes elfective. cylinder 50 (Fig. 3) of two inch diameter in the present instance since this is the diameter of the rotor chamber, is mounted in the lathe on centers at that are eccentric by one sixteenth of an inch and the reduction in diameter, by turning, is continued until the cylinder is almost one and three-quarters inches in diameter. The work is removed To gain this end a solid from the lathe while a sector 52 of the rotor is still bounded by a curved surface 54 on an arc of exactly one inch radius, although the remainder of its cylindrical surface is on an arc of very slightly in excess of seveneighths of an inch radius. The turning of the rotor is stopped when the one inch radius arc is reduced to about one half an inch in length, since this is suflicient to overlap the far sides of the adjacent air port in either rotor chamber when the contact surface of the rotor is opposite.

With this construction the surface 54 on each rotor servesto completely destroy communication between ports 0 and a or ports I) and a when the point of greatest rotor eccentricit is opposite the sliding van'e and to efiectua ly overcome the leakage that necessarily occurs at this time when the rotor ofi'ers merely a line contact. Asa result the evacuation continues evenly and increasingly and the final reading on the gauge shows a substantially perfect vacuum.

The purpose of having the transverse connecting port 0 as close as possible to the sliding vane will now be clear since the length of the contact surface 54 should be as short as possible for the most eflicient operation of the pump. The vane is formed in two parts and the meeting faces, at subsrantially its center, are drilled to receive springs 56 which act to maintain an air tight contact at all times between the vane and rotors.

The pump, in operation, draws the air from the article attached to the tube 42 which passes through port a and into the rotor chamber 12. Here it is forced through port a by rotor 16, the contacting end of the sliding vane compelling the air to travel around the rotor. The air is sucked through port 0 by the rotor 18 and forced by it through the outlet port I) in to the tank above the level of the oil bath. From here it may be removed at will, through the opening 44. i

Particular attention is directed to the horizontal port 0 which, by connecting the rotor chambers below the sliding vane, permits the series operation of the two rotors on the same body of air. Those sln'lled in the art will recognize at once the immensely greater efii ciency of a tandem construction in which one pump supplements the other, over a superficially like construction in which t e ports are so arranged that the two pumpsoperate alternately on different bodies of air. The extreme simplicity of' construction will'be apparent from theforegoing description,

only three parts being required for each pump i. e. the casing forming the cylinder, the rotor, and the rotor vane.

The nature and scope of the present invention having been indicated and the preferred embodiment of the invention having been specifically described, .what is claimed as new, is:--

'1. A tandem vacuum pump comprising a casing having two cylinders, a rotor in each cylinder, a tangent partition wall between said cylinders having a slot therethrough, a common rotor vane slidable in the upper portion of said slot whereby the lower portion below the vane forms a connectingport between the two cylinders, said casing having an inlet port for one pump and an outlet port for the other above said vane, and means for driving. both rotors in the same direction;

2. A tandem vacuum pump comprising a casing having two cylinders, a rotor in each cylinder, a tangent partition wall between said cylinders having a slot therethrough, the major portion of which lies below the plane of the axes of the rotors, a common rotor vane in said slothaving spaced slide legs bearing on the lower wall of the slot and maintaining the vane in the upper portion thereof, whereby the lower portion of the slot forms a connecting port between the two cylinders, said casing havingan inlet port for one pump and an outlet port for the other above said vane, and means for driving both rotors in the same direction.

3. A tandem vacuum pump comprising a casing having two cylinders with a tagent partition wall between them, a rotor'vane common to both cylinders slidably seated in said wall, a connecting port between the cylinders below the vane, an inlet port for one cylinder above one end of the vane and an outlet port for the other cylinder above the other end of the vane, and an eccentrically mounted rotor in each cylinder having a surface contact with the cylinder wall equal in angular length to at least the angular distance between the lower wall of said connecting port and the upper wall'of the other port communicating with the cylinder.

REINOLD BERRENBERG. 

